As someone who has suffered this exact problem (made worse by moving between the US and New Zealand school systems and back, with the different spelling in both), i have mixed feelings on this topic.
On the one hand, it really doesn't seem fair to be judged on spelling in technical classes. I made the exact same complaint many times while in school.
On the other hand, once you get out of school and deal with the real world, people judge you on your spelling, grammar (and capitalization/punctuation as people here reminded me a couple of weeks ago ;-) no matter what you are doing. And in many settings, if you have mistakes in these areas, people stop reading and so your entire message is lost.
Computer spelling and grammar checkers are only somewhat helpful here. They may identify problems, but they make mistakes, and so if you blindly trust them you can get even more confused messages.
So to some extent, this is a critical skill in expressing your ideas to other people, just like typing is a critical skill in getting your ideas into a computer. If you aren't good enough at it, and have to really think about it as you go, the expression of your ideas suffers. When you get "good enough" at it that you aren't thinking about the mechanics and details of it anymore, it frees up a significant chunk of brainpower that instead gets spent on the real problem.
One of the great things about working with the opensource community is that everyone seems much more willing to overlook minor glitches in this area. Part of this is that there are so many people for who english is not their primary language that mistakes are very common. But even here it is a distraction for many people.